Barometric pressure (BP) in an engine intake of a vehicle may vary due to altitude changes of the vehicle. Thus, an accurate assessment of barometric pressure changes experienced by an engine of a vehicle may be beneficial for improved operation of the vehicle. In particular, diagnostic functions, e.g., evaporative emission control system diagnostics, and engine strategies, e.g., air/fuel ratio estimates and spark timing, may benefit from having an accurate estimate of barometric pressure. Barometric pressure is typically determined via either a dedicated BP sensor, or inferred via a manifold absolute pressure (MAP) sensor positioned in an intake of the engine. However, in a condition where the BP sensor is not functioning as desired, or if the BP inference is not correct, such a condition may have adverse effects on engine controls and other diagnostics that utilize the BP data. Accordingly, the BP sensor or surrogate MAP sensor needs to be rationalized per California Air Resources Board (CARE) regulations.
Prior art methods may utilize other engine pressure sensors to rationalize BP. For example, U.S. patent application 7,631,552 teaches a fault condition when the absolute pressure differential between intake manifold pressure and barometric pressure exceeds a calibratable maximum threshold, for a calibratable period of time and a calibratable number of occurrences and a calibratable number of drive cycles. However, the inventors have recognized potential issues with such an approach. As one example, in a case where a vehicle is not equipped with a dedicated BP sensor, but rather BP is being inferred from a MAP sensor, there may be limited options for rationality to other engine sensors. Furthermore, in some approaches a global positioning system (GPS) may be included in a vehicle to determine altitude changes. However, not all vehicles have GPS technology and there may be remote geographical areas where GPS reception is not available. As such, rationalizing BP via GPS technology may be unreliable or costly.
Thus, the inventors herein have developed systems and methods to at least partially address the above issues. In one example a method is provided, comprising delivering fuel from a fuel system to an engine propelling a vehicle; storing fuel vapors from the fuel system in an evaporative emissions control system; determining an estimate of barometric pressure as a function of an efficiency of a vacuum pump configured to evacuate or pressurize the fuel system and evaporative emissions control system; and adjusting a vehicle operating parameter responsive to the estimate.
As one example, determining an estimate of barometric pressure as a function of the efficiency of the vacuum pump includes turning on the vacuum pump and drawing a vacuum across a reference orifice of fixed diameter. The efficiency of the vacuum pump is thus a function of a vacuum level achieved by the vacuum pump when drawing the vacuum across the reference orifice of fixed diameter. In an example, efficiency of the vacuum pump decreases as barometric pressure decreases, and efficiency of the vacuum pump increases as barometric pressure increases. Barometric pressure determined as the function of the efficiency of the vacuum pump is thus correlated with barometric pressure determined from one or more sensor(s) in the vehicle, wherein it is indicated that the one or more sensors in the vehicle are not functioning as desired responsive to a lack of correlation between barometric pressure determined as the function of the efficiency of the vacuum pump and barometric pressure determined from the one or more sensor(s) in the vehicle. In this way, barometric pressure may be inferred by a pump wherein a reference vacuum is drawn across a reference orifice. By inferring barometric pressure using a pump, other barometric pressure sensor(s) in the vehicle may be rationalized, whereby engine strategies that benefit from an accurate estimate of barometric pressure may be improved.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.